The present invention relates to an improved conductor for high voltage transmission line, for example, 230 kV or more. In the present day, the typical high voltage conductor comprises a plurality of conductor wires which are wound helically in a cable. Due to the high voltage, a high electric field is created and directed outward from the conductor surface. Under certain conditions, this leads to the formation of coronas which represents a substantial loss in energy. In addition to the loss of energy, the development of the coronas creates environmental pollution in the form of television and radio interference and objectionable audible noise in the near vicinity of the transmission line. The problem of corona development has been solved to some degree by the substitution of multlple small conductors for the single large conductor.
During periods of above-freezing precipitation, water collects on the top and sides of the conductor and rolls or slides downward to the bottom of the conductor. Eventually, drops of water form all along the bottom of the conductor. Each water drop represents a protrusion from tha outer surface of the conductor. Practically all water drops concentrate the electric field at the drop tip to a degree that exceeds the safety factor which is built into the conductor and coronas develop. For the typical 60 cycle transmission line, the coronas generated on parts of the positive half cycle, 1/120 second duration, are burst pulses, onset streamers, and plume streamers. Trichel pulses occur on the negative half cycle. The plume streamer is the most intense corona and represents the greatest energy loss as well as the most troublesome radio and audible noises from the conductor. Positive and negative coronas are considered to also cause conductor vibration.
In the applicant's considered opinion, coronas and, in particular, plume streamers are the result of three major factors which are in order of importance: the distance out from the conductor to about 4 kV/cm field strength, the protrusion coefficient, and the conductor surface gradient. To a certain strength, the electric field of the conductor sharpens the tip of the drop, thereby intensifying the electric field leaving the tip. With increasing half-cycle voltage a very small particle spray develops. With more voltage corona and spray occurs. Since the bottom water drops flow down the conductor catenary slopes, the highest incident of coronas is on the lower height section of the catenary.
Although the problem of precipitation induced coronas for high voltage conductors has long been recognized, no effective means have been developed for eliminating the problem. One attempt to solve this problem, consists of the application of stalactite-like projections along the bottom of a conductor to collect and discharge water. The projections cannot be applied to the conductor during manufacture of the conductor, since it would interfere with winding of the conductor on the spool so that it would be impractical to store and transport the conductor. Application of the projections after the conductor has been installed is also very difficult and impractical. In addition, the projections would be affected by wind and might initiate vibration of the conductor.
These and other difficulties experienced with the prior art devices have been greatly decreased by the present invention.
It is, therefore, a principle object of the invention to provide a high voltage conductor which is effective in reducing coronas during periods of above-freezing precipitation.
Another object of the invention is the provision of a high voltage conductor which is effective for reducing coronas in moderate and higher rainfalls by shedding water with minor corona generation.
A further object of the present lnvention is the provision of a high voltage conductor which is effective in reducing the negative effects of coronas by reducing their intensities.
It is another object of the present invention to provide a high voltage multi-wire conductor which is effective in reducing coronas during periods of above-freezing precipitation and which can be formed by conventional conductor fabricating apparatus.
A still further object of the invention is the provision of a multi-strand high voltage conductor which is effective in reducing coronas during periods of above-freezing precipitation and which can be stored and transported on conventional spools or reels.
It is a further object of the invention to provide a multi-wire high voltage conductor which is effective in reducing coronas during periods of above-freezing precipitation by employing a protrusion element which is part of the conductor.
It is a further object of the invention to provide a high voltage conductor which is effective in reducing coronas during periods of above-freezing precipitation and which is simple in construction, inexpensive to manufacture, and capable of a long life of useful service.
With these and other objects in view, as will be apparent to those skilled in the art, the invention resides in the combination of parts set forth in the specification and covered by the claims appended hereto.